1. Field of the Invention
This invention relates to a method of powering an electrical circuit. The invention particularly, but not exclusively, relates to a method of operating a circuit including sensing means for sensing the position of a rotor relative to a stator of an electric machine of the kind in which data concerning the position of the rotor relative to the stator is utilized by a motor controller to energize appropriately windings associated with the stator. The invention also relates to associated apparatus.
2. Description of Related Art
Particularly in switched reluctance and brushless types of machine, it is a requirement for the position of the rotor relative to the stator to be known so that the various windings of the stator can be energized at appropriate times, i.e. when respective poles of the stator and rotor are appropriately positioned.
A more detailed description of the switched reluctance machine can be found in the article "The Characteristics, Design and Applications of Switched Reluctance Motors and Drives" by Stephenson et al., PCIM '93, Jun. 21-24, 1993. It will be appreciated that the switched reluctance machine, for example, can be run equally well as a motor or a generator.
Conventionally, the rotor carries a timing disc. A sensor is able to sense the rotational position of the disc and provide an input to an electronic circuit which generates data for transmission to the motor controller where the data is processed. The motor controller energizes a respective winding of the stator in accordance with the position of the stator. The electronic circuit is conventionally powered from a power supply in the motor controller.
In some applications, e.g. where the motor is a compressor motor in an air ventilator and/or air conditioning/circulating system of a vehicle, such as a carriage of a train, it is a requirement for the motor controller to be positioned remote from the motor. Thus, long lengths of cabling are required from the controller to the motor, including cab ling necessary to provide a power supply to the electronic circuit of the sensing means. This introduces the risk of voltage transients and noise being induced in the power supply to the electronic circuit, particularly where the motor controller is located in a hostile electromagnetic environment, where transients may need to be suppressed at either or both ends of the power supply cabling. Both the cabling for the power supply to the electronic circuit and the apparatus required to achieve transient suppression impose a cost penalty.